Process for the production of polyethylene powder having a high density and high tap density

ABSTRACT

A process for the production of polyethylene powder of high density and tap high density comprising polymerizing ethylene at a temperature of from 20*C to 200*C and a pressure of from 1 to 100 atmospheres in the presence of a catalyst prepared from (a) organo-silicon compounds with silicon-hydrogen bonds, (b) compounds of heavy metals of the IV to VI sub-group of the Periodic System, and (c) optionally, compounds of metals of the III main group of the Periodic System characterized in that the prepared catalyst, before polymerization, is treated at a temperature from -40*C to +60*C with oxygen for a time sufficient that from 1 percent to 70 percent, preferably from 5 percent to 50 percent of the compounds of heavy metals of the IV to VI subgroups of the Periodic System present in a lower valence are oxidized to their highest valence and, optionally, the oxidized catalyst is further activated by the addition of monomeric and/or polymeric organic compounds of silicon and/or tin.

United States Patent [191 Piekarski et a1.

1 1 PROCESS FOR THE PRODUCTION OF POLYETHYLENE POWDER HAVING A HIGH DENSITY AND HIGH TAP DENSITY [75] Inventors: Gottfried Piekarski; Anton Hundmeyer, both of Burghausen,

Germany [73] Assignee: Wacker Chemie GmbH, Munich,

Germany [22] Filed: May 16, 1972 [52] U.S. Cl. 260/943 C, 252/429 A, 252/429 B, 252/429'C, 260/949 E [51] Int. Cl. COSI' 1/44, C08f 3/06 [58] Field of Search 252/429 B; 260/949 C, 260/949 E [56] References Cited UNITED STATES PATENTS 2,974,133 3/1961 Wiberg et a1. ..'260/94.9 C

3,202,617 8/1965 Enk et a1 1. 260/949 E 3,227,702 1/1966 Small et a1. 260/949 B 3,328,378 6/1967 Piekarski et al 260/949 E 3,676,418 7/1972 Tashiro et a1. .1 260/949 C FOREIGN PATENTS OR APPLICATIONS 845,878 8/1960 GreatBritain 1,122,157 7/1968 Great Britain 854,988 11/1960 Great Britain 828,201 2/1960 Great Britain 222,426 6/1959 Australia 838,028 6/1960 Great Britain 860,407 2/1961 Great Britain Primary Examiner-Joseph L. Schofer Assistant ExaniinerEdward J Smith Attorney, Agent, or Firm-Hammond & Littell 7] ABSTRACT A process for the production of polyethylene powder of high density and tap high density comprising polymerizing ethylene at a temperature of from C to 200C and a pressure of from 1 to 100 atmospheres in the presence of a catalyst prepared from (a) organosilicon compounds with silicon-hydrogen bonds, (b)

compounds of heavy metals of the IV to V1 sub-group of the Periodic System, and (c) optionally, compounds of metals of the 111 main group of the Periodic System characterized in that the prepared catalyst, before polymerization, is treated at a temperature from C to +C with oxygen for a time sufficient that from 1 percent to percent, preferably from 5 percent to 50 percent of the compounds of heavy metals of the 1V to V1 sub-groups of the Periodic System present in a lower valence are oxidized to their highest valence and, optionally, the oxidized catalyst is further activated by the addition of monomeric and/or polymeric organic compounds of silicon and/or tin.

13 Claims, No Drawings- PROCESS FOR THE PRODUCTION OF POLYETHYLENE POWDER HAVING A HIGH DENSITY AND HIGH TAP DENSITY THE PRIOR ART Low pressure polyethylene powder, obtained from polymer suspensions, generally occurs as a light powder of low density, for example, 100 to 400 gm/l (determined with the Stampfpulvometer [Tap-pak Volumeter] of J. Engelmann AG., Ludwigshafen a. Rh.; 60 blows in 16 seconds). In the region-of the higher tap densites, these powders also Contain considerable amounts of fines of below 70 M grain size, which are undesirable in most cases of processing. If the polyethylene powder is obtained from melts, solutions or also from the gas phase, it is usually coarser, but has, however, a very porous grain of high specific surface (determination, according to BET) of, for example, m /gm. The tap density of these powders amounts at most of 380 gm/l. The direct processing of such poly-' ethylene powders to molded bodies is possible, if at all, only on special machines.

For these reasons it is generally customary to granulate low pressure polyethylene powder, obtained by known processes, before processing them to molded bodies or to subject them to another, always expensive, condensation or sintering process (see French Pat. No. 1,426,438 and DAS 1,189,700).

In order to raisethe polymer tap density, it has al-' by the addition of a monomeric and/or polymeric organic compound of silicon and/or tin.

A still further object of the present invention is the development of a catalyst for the production of polyethylene powder of high density and high tap density consisting essentially of the reaction product of (a) an organo-silicon compound containing hydrogen bonded to silicon, (b) a compound of heavy metals of the IV to V1 sub-groups of the Periodic system, and (0) optionally, a compound of metals of the III main group of the Periodic System, treated with oxygen at a temperature of from 40C to +60C for a time sufficient that from 1 percent to 70 percent of the heavy metals of the IV to V1 sub-groups of the Periodic System present in a lower valence are oxidized to their highest valence, and (d) optionally, further activated by the addition of monomeric and/or polymeric organic compounds of silicon and/or tin to the oxidized catalyst.

These and other objects of the invention will become more apparent as the description thereof proceeds.

DESCRIPTION OF THE INVENTION A process has now been found for the preparation of polyethylene powder 'of high density and high tap density by polymerization of ethylene at a temperature from 20C to 200C and a pressure from 1 to 100 atmocatalyst which was prepared lyst is treated with oxygen at a temperature of from which were prepared according to DBP 1,191,105 and.

the German Offenlugungsschriften (DOS) 1,545,177 and 1,545,194, partially also high tap densities are obtained, but the dust part of the powder (grain size below 50 1L) is disadvantageously high.

OBJECTS OF THE INVENTION An object of the present invention is the development of a process and a catalyst for the production of polyethylene powder of high density and high t-ap density.

Another object of the present invention is the development in a process for the production of polyethylene powder of high density and high tap density which comprises polymerizing ethylene at a temperature of from 20C to 200C and a pressure of from 1 to 100 atmospheres in the presence of a polymerization catalyst prepared from (a) organo-silicon compounds containing hydrogen bonded the silicon, (b) compounds of heavy metals of the IV to VI sub-groups of the Periodic system, and (c) optionally, compounds of metals of the 111 main group of the Periodic System, the'improve-' -40C to +60C so that 1 percent to percent, preferably 5 percent to 50 percent, of the compounds of the IV'to VI sub-groups of the Periodic System, present in a low valence, are oxidized, and optionally, monomeric and/or polymeric organic compounds of silicon and/or tin are added to the oxidized catalyst.

The oxidation of low pressure polyethylene catalysts, particularly Ziegler catalysts, has in itself been known. According to the DAS 1,074,858, the oxidation of the catalysts is carried out with oxygen. With thiscatalyst polymers are obtained, which exhibit relatively low molecular weights.

It has been further known from the German Auslegeschriften'(DAS) 1,135,176 and 1,204,826, that by treatment of the catalysts with peroxides, catalysts are formed, which lead to polymers with increased molecular weights. I

In comparison to this, by the oxygen treatment of the catalysts containing hydrogen bonded to silicon of the invention, suprisingly, polyethylene powders of high tap 'density where obtained, for example, 450 to 570 gm/ 1 with low specific surfaces (BET) of from 0.25 to 0.4 m /gm and grain size distributions, which have in the range below 50 pt only an amount of 2 percent or less-The powder grain is, therefore, very dense and the tap densities obtained approach those of granulates. The bulk density (according to DIN 53468 in gm/l) is also found correspondingly high. The density of the polyethylene (determined according to DIN 53479 on 1 mm pres sed plates) is, dependent upon the molecularv weight, between 0.940 and 0.965 gm/cm. The polyga'nic compounds of silicon mers of the invention are, therefore, highly dense polyethylene. The dry polymer powder can, on the basis of these properties, be processed on the conventionalprocessing machine directly to the finished article without dust nuisance and without a preceding granulation.

if a so-called Ziegler catalyst (for example. according to DBP 973,626) is oxidized under the conditions of the invention procedure, catalysts, unsuitable for ethylv ene polymerization, are obtained The catalyst of the invention is preferably a catalyst for the production of polyethylene powder of high density and high tap density consisting essentially of the reaction product of (a) an organo-silicon compound containing hydrogen bonded to silicon, (b) a compound of heavy metals of the IV to Vl sub-groups of the Periodic system, and (c) optionally, a compound of metals of the Ill main group of the Periodic system, heated with oxygen at a temperature of from 40C to +60C for a time sufficient that from 1 percent to 70 percent of the heavy metals of the 1V to V1 sub-groups of the periodic System present in a lower valence are oxidized to their highest valence, and (d) optionally, further activated 4 The organo-silicon compounds containing hydrogen bonded to silicon, used in the catalyst preparation, are, for example, tl'iethylsilnne, triethoxysilane. tetramethylsiloxane, tetrametliyleyelotetrasiloxane and hydrogenpolysiloxanes, especially those having the formula:

where R is alkyl having 1 to 6 carbon atoms, cycloalkyl having 5 to 6 carbon atoms and phenyl with the termi nal silicons satisfied with R, hydrogen or, at most, one hydroxyl and having a viscosity of from 5 to' 100 cSt (25C), such as methylhydrogenpolysiloxane. Compounds of the elements of the IV to V1 sub-groups are,

' for example, titantium tetrachloride, titanium trichloable for the catalyst preparation, are, for instance,

specified in German Pat. Nos. 'l,l9l,l05' and 1,214,407 and German Offenlegungsschriften (DOS) 1,545,177, 1,545 ,l84 and 1,545,194. Preferably in the preparation of catalysts, which are subjected to the-oxidatio'maccording to the invention, the work is done without solvents or with only slight amounts of solvents.

Preferably the preoxidized catalyst is the reaction product of l one part by volume of an organosilicon compound containing hydrogen bonded to silicon, (2) from 0.5 to 2.0 parts by volume of a compound selected from the group consisting of halides, lower alkoxides and oxyhalidesof heavy metals of the 1V to Vl sub-groups of the Periodic System, and preferably titaride in mixture with titanium tetrachloride, the addition complex Antct vanadium oxychloride, vanadium tetrachloride and chlorotitanic acid esters, such as trichlorotitanic acid butyl ester, etc. Compounds of the 111 main group are, for example, aluminum chloride and aluminum bromide.

The oxidation of the catalyst or the catalyst suspension is carried out preferably by treatment with oxygencontaining gases, particularly air, at temperatures from 40 C to +60C, preferably at 0 to 40C. The dry gas is introduced in a measured amount and .during a definite time through the stirred catalyst suspension. The required amount of the oxidation depends on the amount of the low valence elements of the sub-groups, such as Ti or V***, present in the catalyst, which is determined by titration, and ;,the selected oxidation temperature. Whenl percent'fo 70 percent, preferably 5 percent to SO'percent, of the lower oxidation stage nium, vanadium and chromium compounds, and (3) from 0 to 0.2 parts by volume of an aluminum compound selected from the group consisting of aluminum halides, aluminum lower alkoxides and lower alkyl aluminums, preferably aluminum trihalides, aluminum trilower-alkoxides and tri-lower alkyl aluminum. The catalyst is prepared by mixing the metal halides and/or alkoxides, and the organo-silicon compounds containing hydrogen bonded to silicon, as well as the optional aluminum compounds under good agitation, for instance,

with a vihromixer; perhaps in the presence of small compounds, present in the catalyst suspension, are oxidized to the higher oxidation stage, the oxidation is terminated. Aftertheoxidation, preferably a dry inert gas, such as nitrogen or argon is bubbled through the suspension. The amount of inert gas used should be more than half of the amount of oxygen applied. This posttreatment is carried out for a few minutes, mostlyabout five minutes at room temperature.

The catalyst, treated with oxygen orwith air, shows in the polymerization of ethylene at normal pressure already a relatively high activity. An increase in activity that is, a smaller amount of oxidized catalyst at equal space-time-yield of polymer product, can be attained by the addition of slight amounts of monomeric and/0r polymeric organic compounds of silicon and/or tin. Thereby advantageously amounts between 0.1 to 30 percent by weight, based on the oxidized catalyst, are utilized. Preferably, monomeric silanes with at least one hydrogenatom bonded to silicon, particularly triethylsilane and/or tetraalkyl tin, particularly tetrabutyl tin, are used. Further examples of such compounds are diphenylsilane, tetrarnethyldisiloxane and tin tributylhydride. Also polymeric silicon compounds of various chains length are of importance, preferably hydrogenpolysiloxane compounds in the viscosity range from 2 to 50,000 cSt (25C) with structural units of the general formula:

wherein R 'i-c i taat ztsapsaaan stagnated alkyl or phenyl radical. particularly methylhydrogenpolysiloxane.

The addition of these compounds can be carried out immediately after the inert gas rinsing or also together with the diluting agents, such as hydrocarbons, before or during the polymerization.

The process for the preparation of polyethylene powder of high density and high bulk weight can be conducted both discontinuously and also continuously. Preferably the work is done thereby at temperatures between 50 to 90C and at ethylene pressures from 5 to atmospheres. Furthermore, also modified polyethylenes with the use of the oxidized and optionally activated catalysts can be prepared. For this, together with ethylene, up to l0 mol percent, based on the ethylene, of a higher oz-olefin having 3 to 6 carbon atoms, such as propylene, butene-l or hexene-l are used for the polymerization.

tion Ser. No. 152,761, filed June 14, 1971, now US.

Pat. No. 3,775,389) with alcohol for the decomposition and solution of the catalyst, then the polyolefin is separated from the liquid phase and dried.

7 Another advantage of the claifriedprocess consists in that with the use of the catalysts, according to the invention, polymerizations with high solid-content concentration can be conducted, for example, the polymer suspension at a concentration of percent by weight of polyethylene is still relatively thinly liquid and can be stirred easily. Thereby no precipitates occur and the available reaction space can be utilized better, whereby the production is increased.

It was further found that the oxidized catalyst can be very easily dissolved out of the polyethylene. Thus polymerizates with a slight residual ash content and better properties are obtained. In addition, lesser amounts of stabilizer additives are required.

The polyethylene powdersjprepared according to the invention, can be utilized, on the basis of their high tap density, the high grain density and the good flowability or a relatively coarse grain size, as well as based on the low specific surface, which causesonly a slight gas adsorption, on the various processing machines, such as presses, extruders, flame sprayers, injection molders and rotary casting processes, and for sintering coating. High quality molded products with excellent mechanical properties are obtained thereby.

The following examples are illustrative of the invention without being limitative.

EXAMPLE 1 In a dry glass vessel with a nitrogen atmosphere, 54.7 ml of methylhydrogenpolysiloxane having a viscosity of 30 cSt at 25C, 0.55 gm of AICL, and 55 ml of paraffin hydrocarbons having a boiling range of l 10 to l45(. were heated with agitation to 50C. After 15 minutes the AlCL, was completely dissolved. Then 54.7 ml of TiCl, were added and heated under vigorous agitation with a vibromixer for 6 hours at 50C. A dark-brown suspension was formed and 35 percent of the charged TiCl, had been reduced. After cooling to 20C and diluting with paraffin hydrocarbon to a total volume of 200 ml, dry oxygen was introduced during 20 minutes at 30C in an amount of 20 l/hr (rotameter) with the aid of an immersion capillary causing a weak agitation. As the oxidation is exothermic, occasionally cooling had to be applied. Rinsing with 40 l/ hr of N; was carried out for 7' minutes at 20C in order to terminate the oxidation. The Ti content of the suspension was now 26 percent of the charged Ti ions. The catalyst suspension was poured into a dry l-liter glass flask and diluted with the above solvent to a volume of 0.9 liter.

For the ethylene polymerization, 98 liters of the above paraffin hydrocarbon was charged into a 150- liter. autoclave and heated to 64C. After addition of the above catalyst suspension with rinsing of the flask with 1 liter of isooctane, in which 3.5 ml of tetrabutyl tin were dissolved, the autoclave pressure was adjusted to 10 atm. pressure of ethylene and maintained at this ethylene pressure. The polymerization time was l0%]hours at 64C. During the whole polymerization time the ethylene consumption was very uniform. At the end of the polymerization, the polyethylene suspension was still relatively thin and easy to stir with a concentration of 50 percent (gm polyethylene in gm of suspension). No wall coating was seen in the autoclave and the removal of heat was in no way obstructed.

After decomposition of the catalyst with a mixture of paraffin hydrocarbon/isopropanol/ethanol (vol. percent 60/20/20) at C during /2 hour, separation was carried out on a centrifuge with rinsing with amixture of paraffin hydrocarbons, 5 isopropanol'and 5 ethanol (percent by volume) at 60C. The polyethylene, separated on the centrifuge and rinsed, has about 30 percent less residual moisture in comparison with the same polymerization in which a non-oxidized catalyst was utilized. A total ofonly 4.12 liters of solvent (paraffin hydrocarbon and alcohols) were used for each kg of dry polyethylene recovered. After drying, 68.3 kg of a pure whitepolyethylene powder were obtained with the following properties:

Melt index (DIN 53735, 5 kg load): 0.18 gm/lO min.

Density (DIN 53479): 0.950 gm/crn Oxidation ash: ppm

Tap density: 555 gm/l Bulk density (DIN 53468): 510 gm/l Specific surface (BET): 0.3 m /gm Grain size: 98 percent between 100 p COMPARISON EXPERIMENT If a catalyst, prepared as above, however, nonoxi dized, is used in 10 /2 hours, 62.8 kg of polyethylene were obtained. The polymerization strongly exothermed at the beginning. Near the end of the polymerization, the ethylene consumption showed a sharp decrease. The polymer suspension was already somewhat thick and difficult to stir. Properties of the polyethylene obtained:

Melt index: 0.09 gm/lO min. scribed in Example l, catalyst oxidation: 24 min. at a Density: 0.946 grn/cm rate of 20 liter of (i /hr. at 30C. 'After processing. as Oxidation ash: 180 ppm described in Example l, 32 kg of polyethylene per 24 Tap density: 463 gm/l hours were obtainedhaving the following properties: Specific surface: 0.39 m /gm 5 Melt index: 0.50 gm/lO min. Grain size: 92 percent between 75 and 160 ,u; 6 per- Density: 0.953 gm/cm" cent greater than l60 t; residue less than 75 u. Oxidation ash: 140 p m Tap density: 5l0 gin/1 EXAMPLE 2 Grain distribution: 95 percent between Hit) and l50 Proceeding as described in Example I, however, t, without the addition of the tetrabutyl tin, the yield of 1.5 per n PM Polyethylene was reduced w g lhe Slime P y" For each kg of dry polyethylene in this experiment, mel'llailfln time- The melt index of the polycthylcilc 7.1 liters of solvent were used in the cycle. rose to 0.47 gm/ l 0 min. The other properties were similar to identical. The density was up at 0.952 gm/cm, is EXAMPLE 13 also the oxidation ash, through the lower yield, was up w to 50 ppm 2 kg of the polyethylene was Screened on A polymerization experiment, condu ct ed analogous a Swing sieve during 1 min at 300 mesh and a residue to Example l2 can carried out at 85 C. without stir- V of 4 gm 02 percent was Obtained. It was remarkable rmg and deposit difficulties at a concentration of 45.5 that no dust nuisance Occurred. percent. Only 5.5 liters of solvent were required'inthe cycle for each kg of polyethylene. The obtained poly- EXAMPLE 3 TO ll ethylene. 4| .3 kg per 24 hour. had the following prop- Three catalysts, each weighing 30 gm, were used at 7 various polymerization temperatures for ethylene poly- Melt gm/m merization in a liter autoclave: 25 P BY 9-963 gill/Cm" v Oxidation ash: 130 ppm Tap density: 500 gm/ 1 Catalyst A Example ll miidmimi- Grain distribution: 97 percent between 70 and 160 1.1., without tetrahutyl tin l t 50 1 Catalyst 8 (as Example I) With oxidation, percen without tetrabutyl tin I Catalyst C (as Example l .With oxidation.

with 0.4 ml of tetrabutyl tin EXAMPLE l4 Polymerization conditions lO'atm. of ethylene. varied i.

pmymcrizmkm mmpcmwms A catalyst was prepared from 5 ml of methylhy v as given drogenpolysiloxane having a viscosity of cSt at Disperskm t" i l hydm 25C, 0.3 gm of AlCl and 5 ml of TiCl by agitating carbon with a hmhngrange s D fmm m w 4u( at C during 5 hours. After the dilut on of the catalyst suspension with 5 ml of paraffin hydrocarbon hav-. The results are given in the following table. g a bOiliflS range of 1 t0 l dried Over TABLE I T Polymerization Space Melt lndex Temperature kg Time-Yield Tap Density 5 kg Catalyst C Polyethylene gm/l/hr. gm/l grit/l0 min.

A 00 11.7 58.5 472 0.03 B I23 6L5 52l 0.04 B ll.5 57.5 555 0.1 C 60 ll.6 58 532 0.03 A 72 Ill 76.] 44a 0.l2 B 72 l4.1 70.5 490 0.22 C' 72 I39 69.5 520 0.23 A 35 9.9 79.2 390 0.67 C I32 728 490 L Based on 35 liter pot volume. Catalyst oxidation 30 min. instead of 20 min with 20 l/hr. at 30C (22% of'l'l' it can be seen that at'the low est polymerization ternmolecular sieves, was passed through a capillary with perature the highest tap densities were obtained. The 55 cooling and stirring into the suspension at temperature catalysts B and Cwere clearly superior to the catalyst maximum of 36C, with a velocity of 10 l/hr for a pc- A in regard to the packed density of-the obtained polyriod of 40 min. After the oxygen treatment. dry nitroethylene. At the higher polymerization temperatures, gen as passed through the same capillary at 20C at catalysts B and C also give high yields of polyethylene. a rate 0f 1 t for?! period 0f 5 min. e Ti+++ I 60 tent of the catalyst was 40 percent before the oxidation,

27 percent after 20 min. and 20 percent after 40 min.

. 5 EXAMPLE- 12 i of oxidation. v Ethylene w continuously po y z at 65C and 10 percentof the oxidized catalyst was charged tol0 atm. in a 25 liter autoclave-with isooctane as the disgether i h 600 ml f p raffin hydrocarbon into a l persing agent. 4.6' ram fCflK Y n 3 tfi OflSO 65 liter vessel with ethylene for the polymerization at octane were dosed in per hour. The polymer concenlOatm. of ethylene at 75C. After 2 hours and subsetration was 40 gm of -polyethylene for each gm of quent processing and drying 201 gm of polyethylene polymer suspension. The catalyst was prepared as depowder were obtained with a tap density of 454 gm/ 1.

- gm/cm.

COMPARISON EXPERIMENTS TO EXAMPLE l4 lyst was used for the ethylene polymerization, the polymer yield was 198 gm with a tap density ofonly 347 gm/l.

b. A Ziegler catalyst was prepared from 9.3 ml of diethyl aluminum chloride and 5.5 ml TiCl, (1.5 to 1 mol) in 9.3 ml of paraffin hydrocarbon by heating for 90 minutes at 50C under purest nitrogen and diluted with an additional 10 ml of solvent. Then the suspensions were oxidized at 20C, otherwise analogous to Example 14.- An almost clear solution was formed. 17.5 percent of the oxidized and purged with nitrogen catalyst was charged in 1.2 liters of diluent and ethylene at normal pressure and 75C for the polymerization (Combined gas process). No solid polymerizate was formed c. In an anlogous polymerization experiment, at nor mal pressure with a catalyst employed in an amount of 20 percent and oxidized analogous to Example 14, there resulted, however, after a two hour polymerization time, a polyethylene yield of 215 gm. v

d. lf, for the polymerization. analogous to Example 14 of (c) above, 1.5 percent of the Ziegler catalyst,

oxidized as (b) above, was added, the polymerization speed of the ethylene was clearly reduced and only 82 gm of polyethylene with tap density of 403 gm/l were obtained. i

EXAMPLE 15 The preparation of the catalyst was carried out, as described in Example 1. lsooctane was used as the diluent. The catalyst oxidation was conducted at 10C with 20 l of /hr. fora period of 60 min. and 13 percent of the Ti was oxidized. The ethylene polymerization was conducted as in Example 1, but with a polymerization temperature of 60C. For the activation of the catalyst. ml of the same hydrogenpolysiloxane were added at the start of the polymerization. After processing and drying 67.5 kg of white polyethylene powder were obtained in a space-time-yield of 45 gm/l/hr.

PROPERTIES:

Melt index: (5 kg): 0.04 Density: 0.948 gm/cm Tap density: 521 gm/l EXAMPLE 16 The polymerization and catalyst preparation were conducted analogous to Example 15, but'the catalyst was oxidized, however, for only'30 minutes and 7.7 percent of the Ti ions were oxidized.

73.8 kg of polyethylene were obtained in a spacetime yield of 53.5 gm/l/hr.

PROPERTIES: 1 Melt index (5 kg): 0.05 7 Density: 0.948 gm/cm" Tap density: 510 gm/l The polyethylene powder can be processed on a double screw extruder or on a'planet roll extruder to give pipes of extreme impact tenacity and strength.

- ethylene powder by the injection molding process with- COMPARISON EXPERlMENT To EXAMPLE 16 A non-oxidized catalyst polymerized ethylene under the above conditions only to a yield of 52.3 kg. with a l l a. If, analogous to Example 14, a non-oxidized cata- 5 weld of 35 gm/ hr PROPERTIES;

-Me1t index 5 kg): 0.05 Density: 0.948 'gm/cm Tap density: 450 gm/l EXAMPLE 17 The compounds listed in Example 1 were used for the catalyst preparation. The oxidation of the catalyst suspension was carried out at 30C with 95.5 l/hr. of dry air for aperiod of 15 minutes and 8 percent of the T1 Ht ions were oxidized. After diluting to 0.9 liters. 5 m1 of triethylsilane were added with agitation.

After transfer to the polymerization autoclave, the polymerization was carried out as in Example 1', however at a temperature of 825C. 68.3 kg of polyethylene were obtained in a space-time-yield of 43 gm/l/hr with the following properties: i

Melt index (5 kg): 4.8 gm/10 min.

Density: 0.958 gm/cm Tap density: 543 gm/l Grain size: 94 percent between 100 and 160 p.

Residue 160 ,u. 7

Molded bodies with great impact tenacity. and crack resistance to tension can be produced from this polyout difficulty.

EXAMPLE 18 The catalyst preparation and polymerization'was'as in Example 17, however, instead of triethylsilane, 3.8

ml of tetrabutyl tin were added dropwise to the catalyst after oxidation. After an ethylene polymerization at C, 71 kg of polyethylene were obtained with the following properties: I

Melt index '(5 kg): 1.1

Density: 0.956 gm/cm" v Tap density: 550 gm/l v Grain size: '92 percent between and M v 7 percent 160 ,u 1 percent 100 t.

Towards the end of the polymerization the charge was still well stirrable. No polymer deposits were observed on the walls or the agitator of the reactor.

The polyethylene powder can be processed on the conventional flame spray machines without difficulties to give hollow bodies of any kind. 7

The preceding specific embodiments are illustrative of the practice of the invention. It is to be understood, however, that other expedients known to those skilled gm/lO min.

in the art or disclosed herein, may be employed without Si -O where R is a member selected from the gro up consisb ing of alkyl having 1 to 6 carbom atoms. cycloalkyl having 5 to 6 carbon atoms and phenyl, with the terminal silicons satisfiedwith R, hydrogen or, at most, one hydroxyl and having a viscosity of from 5 to 100 cSt (25C), (b) about 0.5 to 2.0 parts by volume of a compound selected from the group consisting of titanium tetrachloride, titanium trichloride in mixture with titanium tetrachloride and the addition complex AlTi Cl and (c) about to 0.2 parts by volume of a compound selected from the group consisting of aluminum chlo ride and aluminum bromide, treated, in the presence of from 0 to 2 parts by volume of a saturated hydrocarbon having to 9 carbon atoms, with oxygen at a temperature of from -40C to +60C for a time sufficient that' wherein R is a'membe'r selected from the group consisting of alkyl having 1 to 6 carbon atoms and phenyl, and having a viscosityof from 2 to 50,000 cSt (25C), to the oxidized catalyst.

2. The catalyst of claim I wherein said component (a) is methylhydrogenpolysiloxane having a viscosity of from 5 to 1000s: (25C), said component (b) is'titanium tetrachloride, and said component (c) is aluminum chloride. 1

3. A process for the preparation of the catalyst of claim 1 which consists essentially of reacting said components, (a), (b), and (c) at a temperature of from C to 80C under an anhydrous inert atmosphere until hydrogen evolution has ceased. treating said reaction product. with oxygen at a temperature of'from' 40C to +60C for a time sufficient that from 5 'p'ercent to 50 percent of the titanium ions present in a lower valence are oxidized to their highest valence, and recovering said catalyst.

4. In a process for the production of polyethylene powder of high density and high tap density which comprises polymerizing ethylene at a temperature of from 20C to 200C and a pressure oil from i to l00 atmospheres in the presence of apolymerization catalyst prepared from (a) about I part by volume of a hydrogenpolysiloxane with structural units having the forrnula a ing of alkyl having 1 to 6 carbon atoms, cycloalkyl havtin, tetramethyldisiloxane, tin tributylhydride and 'hy- I where R is a member selected from the group consisting 5 to 6 carbon atoms and phenyl, with the terminal silicons satisfied with R, hydrogen or, at most, one hydroxyl and having a viscosity of from 5 to cSt (25C), (b) about 0.5 to 2 parts by volume of a compound selected from the group consisting of titanium tetrachloride, titanium trichloride in mixture with titanium tetrachloride and the addition complex AlTi Cl and (c) about 0 to 0.2 parts by volume of a compound selected from the group consisting of aluminum chloride and aluminum bromide, the improvement which consists in treatingsaid prepared catalyst in the presence of from O to 2 parts by volume of a saturated hydr'ocarbon having 5 to 9 carbon atoms, before said polymerization, with oxygen at a temperature of from -40C to +60"-C for a time sufficient that from S-percent to 50 percent of the titanium ions present in a lower valence are oxidized to their highest valence and (d) further activating the oxidized catalyst by the addition thereto of from 0 to 30 percent. by weight, based on said oxidized catalyst, of a monomeric and/or polymeric organic compound of silicon and/or tin selected from the group consisting of monomeric silanes with at least one hydrogen atom bonded to silicon, tetraalykl drogenpolysiloxane with structural units-having the formula wherein R is a member selected from the group cons'isting of alkyl having 1 to 6 carbon atoms and phenyl, andhaving a viscosity of from 2 to 50,000 cSt (25C).

wherein R is a member selected from the group consisting of alkyl and having 1 to 6 carbons and phenyl.

10. The process of claim 4 wherein anhydrous air is employed as the source of said oxygen.

[1. The process of claim 4 wherein said oxidized catalyst is treated with an inert gas after said oxygen treatment.

12. The process of claim 4 wherein'said treatment wit h oxygen is effected at a temperature between'O and 40 C.

13. The process of claim 4 wherein said component (a) is methylhydrogenpolysiloxane having a viscosity of from 5 to 100 cSt (25C). said component (b) is titanium tetrachloride, and said component (c) is aluminum chloride. 

1. A CATALYST FOR THE PRODUCTION OF POLYETHYLENE POWDER OF HIGH DENSITY AND A HIGH TAP DENSITY CONSISTING ESSENTIALLY OF THE REACTION PRODUCT OF (A) ABOUT ONE PART BY THE VOLUME OF A HYDROGENPOLYSILOXANE WITH STRUCTURAL UNITS HAVING THE FORMULA
 2. The catalyst of claim 1 wherein said component (a) is methylhydrogenpolysiloxane having a viscosity of from 5 to 100 cSt (25*C), said component (b) is titanium tetrachloride, and said component (c) is aluminum chloride.
 3. A process for the preparation of the catalyst of claim 1 which consists essentially of reacting said components, (a), (b), and (c) at a temperature of from 20*C to 80*C under an anhydrous inert atmosphere until hydrogen evolution has ceased, treating said reaction product with oxygen at a temperature of from -40*C to +60*C for a time sufficient that from 5 percent to 50 percent of the titanium ions present in a lower valence are oxidized to their highest valence, and recovering said catalyst.
 4. In a process for the production of polyethylene powder of high density and high tap density which comprises polymerizing ethylene at a temperature of from 20*C to 200*C and a pressure of from 1 to 100 atmospheres in the presence of a polymerization catalyst prepared from (a) about 1 part by volume of a hydrogenpolysiloxane with structural units having the formula
 5. The process of claim 4 wherein said component (d) is present in an amount of from 0.1 percent to 30 percent by weight based on said oxidized catalyst.
 6. The process of claim 5 wherein said component (d) is triethylsilane.
 7. The process of claim 5 wherein said component (d) is tetrabutyl tin.
 8. The process of claim 5 wherein said component (d) is methylhydrogenpolysiloxane.
 9. The process of clAim 5 wherein said component (d) is hydrogenpolysiloxane having a viscosity of 2 to 50,000 cSt (25*C) and a partial formula
 10. The process of claim 4 wherein anhydrous air is employed as the source of said oxygen.
 11. The process of claim 4 wherein said oxidized catalyst is treated with an inert gas after said oxygen treatment.
 12. The process of claim 4 wherein said treatment with oxygen is effected at a temperature between 0 and 40*C.
 13. The process of claim 4 wherein said component (a) is methylhydrogenpolysiloxane having a viscosity of from 5 to 100 cSt (25*C), said component (b) is titanium tetrachloride, and said component (c) is aluminum chloride. 